Ink-jet printing has become a popular method of recording images on various media surfaces, particularly paper, for a number of reasons, including, but not limited to, low printer noise, capability of high-speed recording, and multi color recording. Additionally, these advantages of ink-jet printing can be obtained at a relatively low price to consumers. Though there has been great improvement in ink-jet printing, improvements are followed by increased demands from consumers for higher speeds, higher resolution, full color image formation, increased stability, etc.
As new ink-jet inks and print engines are developed, several traditional characteristics are considered when evaluating the ink in conjunction with a print medium. Such characteristics include edge acuity and optical density of the image on the print medium, gloss, scratch durability, black to color bleed control, dry time of the ink on the print medium, adhesion to the print medium, lack of deviation in ink droplet placement, presence of all dots, resistance of the ink after drying to water and other solvents, long term storage stability, and long term reliability without pen material degradation or nozzle clogging. Though the above list of characteristics provides an illustration of factors to be optimized for improved ink-jet printing, there are challenges associated with satisfying all of the above characteristics. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, traditional commercial inks for use in ink-jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed characteristics.
One characteristic of ink-jet printing systems that is desirable to achieve is related to frequency response of the ink-jet ink, which is often proportional to ink throughput. Smaller drop sizes have increased the demand for higher frequency printing. With respect to this aspect, obtaining increased printing speed while retaining acceptable print quality is a constant challenge in the ink-jet printing industry.
For example, acceptable print quality is often difficult to achieve when pigment-based ink-jet inks are used in ink-jet printing systems to print color images on photo media. Photo media used with ink-jet printers generally include sheets that are similar to the base paper used in traditional silver-halide photographs so as to replicate the look and feel of traditional photographs. However, ink-jet printers with fast output speeds require photo media that absorb ink and dry quickly. Hence, some photo media also include one or more porous coatings. These porous coatings include a number of fine particles glued together in such a way that there are air spaces or pores in between them. These air spaces are later filled with ink and dyes as the water evaporates and facilitate relatively fast absorption and drying times.
However, while pigment-based ink-jet inks have good permanence properties when used on porous photo media, such inks often suffer from poor gloss and scratch durability. Accordingly, investigations continue into developing pigment-based ink formulations that can be printed accurately at high frequencies, and which have good gloss and scratch durability characteristics.